756 E. C. ANDREWS 



Browne, 1 however, inclines to the belief that a portion of this 

 area, at least, is of Ordovician age. Other schist masses exist in 

 Queensland. 



The possibility of sediments and other rock masses being molded 

 onto, or being wrapped round, these resistant blocks is thus sug- 

 gested. 



Cambro-Ordovician. — Since the momentous pre-Cambrian period 

 the greater portion of the area mentioned appears to have been a 

 positive or buoyant element till the present day. A great negative 

 area appears to have existed at this time over Eastern Tasmania, 

 Victoria, and New South Wales. It is possible, however, that a 

 positive element existed in this period in Southeastern Victoria and 

 New South Wales. The Cambrian sediments are more in evidence 

 on the western strip of this area, while the Ordovician are common 

 on the southeastern and eastern portions. It is possible that the 

 Ordovician sediments of the more eastern areas are conformable to 

 the Cambrian, but there is an unconformity between the shallow 

 water forms of the two in the MacDonnell Ranges of Central 

 Australia. 



Silurian. — At the close of the Ordovician there was a very 

 powerful folding movement. Wherever the Ordovician occurs in 

 New South Wales or Victoria, it is strongly folded and altered. The 

 new land surface was carried far to the north and east by this fold- 

 ing movement. Ordovician sediments occur quite near the coast 

 about ioo miles south of Sydney, and they outcrop within 120 

 miles (lat. 33 S.) of Sydney in a direction west-northwest. Thence 

 to the pre-Cambrian outcrops of the more western areas they may 

 be seen in many places, exposed by the stripping of their Devonian 

 cappings. 2 In the majority of the localities observed the strike of 

 the sediments is west of north. 



During the Silurian the old negative area which had been occu- 

 pied by the Cambro-Ordovician sediments once more sank, and the 

 sea transgressed far to the west, almost to Broken Hill (long. 141 



1 W. R. Browne, "The Geology of the Cooma District, N.S. Wales," Jour. Proc. 

 Roy. Soc. N.S. Wales, XL VIII (19 14), 172-222. 



2 E. C. Andrews, "The Canbelego Gold and Copper Field," Mineral Resources, 

 No. 18, Dept. Mines, N.S. Wales, 1913. See maps and sections. 



